High-frequency-corona-discharge furnace



C. T. ALLCUTT HIGH FREQUENCY CORONA DISCHARGE FURNACE Filed Oct. 27.1923 F/y n INVENTOR Ueser Z'H//ca' ATTORNEY .Sept 29, 1925.

WITN EsSEs:

lPatented Sept. 29, 1925.

UNITED STATES asma PATENT OFFICE.

CHESTER T. ALLCUTT, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T WESTING-HOUSE ELECTRIC l&z MANUFACTURING COMPANY, A CORPORATION O'F PENNSYL-VANIA.

HIGH-FREQUENCY-CQRCNA-IDISCHARGE FURNACE.

Application filed October 27, 1923, Serial No. 671,1.

To all whom z't may concern.'

Be it known that I, CHESTER T. ALLCU'rr,

a citizen of the United States, and a resident of Pittsburghf in thecounty of Allegheny 6 and State of Pennsylvania, have invented a new anduseful Improvement in High-Frequency Corona Discharge Furnaces, of whichthe following is a specification.

My invention relates to electric heating and it has for its object toprovide a method of and means for heating bya high-frequency coronadischarge.

In practicing my invention, I provide a source of high-frequency currentsupply of suiiiciently high voltage to produce a corona dischargebetween a pair of co-operating electrodes and adjacent to a mass ofmat-erial to be heated thereby.

In the single sheet of drawings,

Figure 1 is a schematic View of a heating system embodying my invention,the furnace part thereof being shown in section,

Fig. 2 is a schematic view of a modified form of heating systemembodying my in- 25 vention,

Fig. 3 is a view in vertical section of an electric furnace for use withmy system, and

Fig. 4 is a top plan view thereof.

Referring more particularly to Fig. 1 of the drawing, a container 11 fora mass of material 12 to 4be heated, may be built up of any suitablerefractory material that will resist a relatively high temperature. Thecontainer is preferably composed of conducting refractory material, suchas graphite, although a non-conductingl material may beemployed,particularly if the'.charge 12 is of conducting material. A circularelectrode 13 surrounds the container 11 and is spaced therefrom asuitable distance. The inner peripheral surface of the electrode 13 maybe provided with a plurality of inwardly projecting points 14.

The electrode 13, which is of a suitable electric-'conducting material,is connected to one terminal of the secondarywinding of a transformer15, the other terminal of which is connected to the crucible 11 and alsoto the charge 12 placed therein. The transformer 15 is intended toschematically represent a source of sustained electric current of highvoltage and of high frequency, and I have included a condenser 16y inparallel circuit relation to the secondary winding of the transformerand the furnace constituted by the container 11 and thelelectrode 13 toneutralize the inductive reactance of the transformer 15.

If the source of supply 15 is suitably energized, a relativelyhigh-frequency and high-voltage electric current is delivered to theelectrodes constituted by the member 13 and the member 11 and if thevoltage is sufficiently high, the air becomes ionized and .a coronadischarge is produced at the points 14. This discharge is of relativelyhigh temperature and the heat therefrom Will be radiated or otherwisetransmitted through the crucible 11 to the mass 12 of material locatedthereon, which is to be heated.

It is desirable, in heating systems of this kind, to stabilize thedischarge as otherwise the electrical discharge may take the form of a sark discharge between a relatively few mts on the surface of thelelectrodes and t ereby cause local heating.

In Fig. 2 of the drawing, I have illustrated a construction comprising acontainer 11 with a mass of material 12 located therein. An electrode 17of metal may be located closely adjacent to and around the outer surfaceof a crucible 18 of a dielectric material, such as quartz and spacedfrom the outer surface of the crucible 11. j

The quartz crucible acts as a condenser in series with the ionized airgap between it and the container 11. The action of the condenser is suchas to prevent a spark discharge being established over any individualportion of the electrode or of the material-containing crucible. Theprevent1on of a spark discharge is desirable, since such a dischargewould occurl between a few points Y only on the opposing surfaces of theelectrodes-and would cause localized heating.

vIn Figs. 3 and 4, I have illustrated a relatively simple electricfurnace structure that may be employed in the system embodying myinvention. The inner cruclble and electrode 11 containing the mass 12 ofmaterial to be heated is made relatively small in lateral cross-sectionand may be made relatively deep to receive the desired amount ofmaterial at one time. An Vouter electrode 19 is formed in the shape of acrucible and is of much larger area of cross-section than the container11. A mass 21 of porous re` fractory electric-insulating material, suchas pared to the dimensions of the outer electrode 19, the coronadischarge will be established upon the surface of the inner electrodecontainer 11 when the terminals of a suitable source of supply ofhigh-frequency and high-voltage electric energy is connect-v ed to therespective electrodes. This condition exists for the reason that theelectric stress at any point on the surface ofthe inner electrodecontainer 11 vis very much greater than that on a corresponding andco-operating surface portion of the outer electrode 19. Hence, thecorona discharge will be established on substantially the outer surfaceof the container 11 and the4 heat generated thereby will be transmittedthrough the walls of the container to the mass of material to lbe heatedthat is located therein.

That portion of the air path lying between the electrode 19 and theouter limits of the corona discharge formed on the outer surface of thecrucible 11 is substantially unionized and hence acts as a relativelyperfect condenser dielectric for stabilizing the corona discharge. v

Where I have referred 'to a high frequency alternating current, I desireit to be understood that reference is made to frequencies not less thanthose usually employed in radiotelegraphy and radiotelephonyy and suchhigher frequencies as may be commercially produced for suchapplications. An alternating current of sustained high frequency isparticularly a plicable for my purpose, as the discharges rom a seriesof high frequency wave trains, such as produced by an oscillatory sparkdischarge will not effect the desired heating.

Various modications and changes may be made without departing from thespirit and scope of the invention, I desire, therefore, that only suchlimitations shall be placed thereon as are imposed by the prior art orare set forth in the appended claims.

I claim as my invention:

1. In a heating system, in combination, a` crucible for containing a.charge to he heated, and means for producing a corona discharge adjacentto said crucible to heat the same.

2. In a heating system, in combination, a crucible for containing acharge to be heated, and means for producing a high-frequency coronadischarge adjacent to said crucible' to heat the saine.V

3. An electric furnace comprising a charge to be heated and means forproducing a corona discharge adjacent thereto to heat the same.

4. An electric furnace comprising a charge to be heated and means forproducing a high-frequency corona discharge adjacent thereto to heatthe'same.

5. In a heating system, in combination, a crucible for containing acharge to be heated, an electrode adjacent Ato said crucible and spacedtherefrom, and means electrically connected to said crucible and saidelectrode for producing a corona discharge adjacent to said crucible forheating the same.

6. In a heat-ing' system, in combination, a

'material container of relatively small external dimensions; anelectrode, of relatively large dimensions, surrounding said container,and means for producing an alternating electric field of high potentialbetween said container and said electrode.

7. The method of heating material which comprises the vproduction of acorona discharge adjacent to a crucible containing said material.

8. The method of heating m'aterial which comprises placing a cruciblecontaining the same in a high-frequency electric field of sufficientlyhigh voltage to produce a corona discharge adjacent to said crucible.

9. In a heating system, in combination, a crucible for containing acharge to be heated, means for producing a corona discharge from saidcrucible to heat the same and means for stabilizing said coronadischarge- 10. In a heating system, in combination, a crucible forcontaining a charge to be heated, means for producing a corona dischargefrom said crucible to heat the same and means for insuring asubstantially uniform ditribution of heating ei'ect over said cruci le.

11. In a heating system, in combination, a crucible for containing acharge to be heated, means for producing a corona discharge from' saidcrucible to heat the same and means comprising a condenser for insuringa substantially uniform distribution of current over said crucible.

12. In a heating system, in combination, a crucible for containing acharge to be heated, an electrode adjacent to said crucible and spacedtherefrom, means electrically connected to said crucible and saidelectrode for producing a corona discharge adjacent to said crucible forheating the same, and means located between said crucible and electrodefor stablizing said corona discharge.

In testimony whereof, I have hereunto subscribed my name this 22nd dayof October, 1923. a

CHESTER T. ALLCUTT,

